This invention pertains to adhesive compositions and to composite structures prepared therefrom. In a preferred embodiment, the invention is directed towards a partition for a shipping vessel. The partition is composed of an adhesively bonded composite structure, which preferably is a laminar structure composed of two or more laminae.
Shipping containers and vessels, such as corrugated paper boxes, often require separator boards or partitions to separate the contents of the shipping vessel during transportation in order to protect against damage. Such partitions must be stiff and light in weight in order to provide maximum content protection and in order to minimize packaging cost and shipping weight. Typical separator boards in current use are made from paper products, such as linerboard, a heavy product made from cellulose fibers. Often, the separator boards are made as laminates of these linerboards, the plys of the laminates being held together with one of any number of adhesives currently known to bond cellusosic material together. Typical adhesives used in the construction of linerboard include, for instance, cooked starch, urea-formaldehyde resins, and melamine-formaldehyde resins. The combination of these single and multiple ply separator boards often is a significant portion of the weight of the shipping vessel and may increase shipping costs. In addition, the cost of the partition can contribute to the cost of the final packaged product owing to freight costs in transport of the separator boards from the separator board manufacturer to the shipper.
It has also been proposed to use a partition composed of fiberglass or a like composite material. Fiberglass may be prepared from a nonwoven mat of a fibrous material, typically glass strands or filaments, by impregnating the mat with a thermosetting resin. It has further been proposed to use an adhesive to bind a nonwoven mat of fibers to thereby form a composite structure. A composite structure thus prepared is lightweight and stiff and may be used as a shipping vessel partition, or may be used in the preparation of a laminate. In addition, adhesively bonded laminates are known. In one known process for preparing such a laminate, two mats composed of a nonwoven material are immersed in a bath of an adhesive composition and pressed together. The structure thus prepared is heated to dewater the adhesive composition to thereby form a composite laminate. Through the foregoing process, laminates that have a stiffness that is satisfactory for use in shipping applications can be prepared.
Heretofore, starch-based adhesives have been used to prepare composite structures such as laminates. It has been found that such starch-based adhesives are unsatisfactory in many respects. The composite structure prepared using starch-based adhesives, though lightweight, still are of higher density than ordinarily is desired. In addition, the stiffness of the known composite materials is somewhat unsatisfactory, thus making such materials somewhat unsuitable for use as partitions in shipping vessels.
In light of the foregoing, it is a general object of the invention to provide, in preferred embodiments, a composite material having improved density and stiffness as compared to the known materials heretofore described. More generally, it is an object to provide a method for adhesive bonding, the method being useful in the preparation of composite structures as heretofore discussed.
Surprisingly, it has been found that a hemicellulose-based adhesive can be used in the preparation of composite structures and for other bonding purposes. Hemicellulose is a soluble component of agricultural residue such a corn hulls and other cellulose-containing materials. Hemicellulose is readily obtainable via the alkaline cooking of corn hulls, as is taught in U.S. Pat. Nos. 2,801,955; 3,716,526; 2,868,778; and 4,038,481, and in published International Application No. WO 98US/05551. The alkaline cooking of corn hulls to produce an adhesive composition for cellulosic materials also is known in the art, as is taught in U.S. Pat. Nos. 6,063,178; 5,855,659; and 5,503,668. Additionally, the alkaline cooking of spent corn germ to provide an adhesive composition for cellulosic materials is known in the art, as is taught in U.S. Pat. No. 5,972,091.
In accordance with the invention, a hemicellulose-containing material, such as the liquid fraction from an alkaline-cooked agricultural residue, is used to fabricate a composite structure, such as a laminate. A composite structure thus prepared may be used as a partition in a shipping vessel. As set forth in more detail hereinbelow, the density and stiffness of such structure are improved over those of known composite structures fashioned with starch-based adhesives.
In accordance with a preferred embodiment of the invention, a liquid-pregnable material is impregnated with a hemicellulose-based adhesive composition. The adhesive composition is at least substantially dewatered, such as by applying heat, to thereby form a composite structure. Most preferably, the liquid-pregnable material is one ply (laminae) of a laminar structure, i.e., a laminate. The laminate may be prepared by providing a laminar structure that includes two laminae that are in contact with one another, at least one of the laminae being a liquid-pregnable material that is impregnated with a hemicellulose-containing liquid adhesive composition. Upon dewatering of the adhesive composition, a laminate is provided. Most preferably, the laminate is prepared by providing two laminae, each of which is composed of a nonwoven mat of a fibrous material. Before or after the laminae are placed into contact with one another, but preferably before, the laminae are together impregnated with an adhesive composition. The adhesive composition then is at least substantially dewatered to yield a laminate.
Features of the preferred embodiments of the invention are set forth hereinbelow.